1. Field of the Invention
The invention relates to a frequency modulation (FM) receiver and receiving method thereof, and more particularly to an FM receiver with a signal detector and receiving method thereof.
2. Description of the Related Art
Frequency modulation (FM) is one type of modulation technology in electronic communications, which uses carrier wave frequency variations of a transmitted signal provided by a transmitter to represent data to be sent. Usually, the data to be sent is shown as an electronic signal, such as an electronic signal with voice information, and the amplitude of the electronic signal is reflected on the carrier wave frequency variations of the transmitted signal through FM technology according to a ratio.
In general, an FM broadcast system (radio system) is one type of application for FM technology. At present, the FM broadcast system has a frequency range between 88-109 MHz which comprises 100 channels, wherein a bandwidth of each channel is 100 kHz. A user can use an FM receiver to select a desired channel. Usually, the FM receiver has a function for searching the FM signals. The FM receiver can automatically search the channels one by one to determine whether the radio frequency (RF) signal received in each channel is an FM signal or not, i.e. FM signal search, thus avoiding manual search for the user.
In general, an FM receiver determine whether an RF signal received in a channel is an FM signal or not according to an FM signal to noise ratio (SNR) of the channel. FIG. 1 shows a block diagram illustrating a conventional FM receiver 100. The FM receiver 100 receives an RF signal R. An RF amplifier 110 amplifies the RF signal R, and then a mixer 120 down converts the amplified RF signal R to an intermediate frequency (IF). Next, the RF signal R down converted to the IF may sequentially pass an IF amplifier 130, an amplitude limiter 140 and an FM demodulator 150 so as to obtain a demodulated FM signal. The demodulated FM signal is transmitted to an SNR calculator 180 to calculate a SNR. A signal detector 190 determines whether the RF signal is an FM signal or not according to the SNR and a predetermined threshold. However, because it is difficult to obtain the SNR, the method that uses the SNR determines whether the RF signal is the FM signal or not is deficient. Various methods are used to obtain the SNR, which separate the FM signal and the noise in the channel to calculate the FM signal intensity and the noise intensity so as to obtain the SNR. However, a more complex system is required, thus increasing cost for the FM receiver.
Therefore, an FM receiver and a receiving method thereof are desired to decrease system complexity and cost.